Electric lamp bulb



Feb. 22, 1938. L. E. CALKINS ET AL ELECTRIC LAMP BULB Filed April 8, 1937 INVE NTORS m4 J 10 2 m L W ATTORNEYS Patented Feb. 22, 1938 ELECTRIC LAMP BULB Lyle E. Calkins and Ormonde S. Levi, Toledo, Ohio, assignors to Save Electric Corporation, Toledo, Ohio, a corporation of Ohio Application April 8, 1937, Serial No. 135,736

4 Claims.

This invention relates to bulbs for incandescent lamps, and particularly to those of the inside frosted type.

Inside'frosted lamp bulbs have features of 'advantage in use over outside frosted or other types of light diifusing bulbs, and a considerable demand has resulted in the trade for lamps with such bulbs. In the -past, difficulty has arisen-in the inside frosting of such bulbs due to the frosting methods ordinarily employed, when applied to the inside of abulb, effecting such a weakensioned by the changing of the frosting pits or depressions from sharp angular to rounded form. It is further found, however, that while, such treatment when first applied materially strength- 25 ens such bulbs against breakage, theyweaken with age to such an extentthat within a very few months the bulbs in many cases become so fragile as not to permit commercial handlin without breakage:

80 The object of the invention is the production of an inside frostedelectriclamp bulb of a strength suitable for'commercial handling, which will not Weaken with age, and which will, with a minimum of absorption of light, sufficiently diffuse the emitted light of the associated light source as to prevent any objectionable glare, thus giving maximum light emission, increasing the lamp life at designated efficiency and improving the ultimate lamp quality.

The invention is fully described in the following specification and illustrated in the accomp'anying drawing, in which- Figure 1 is a side view, partly in section, of a lamp bulb embodying the invention, and Fig. 2 is a reproduction of a photomicrograph, enlarged .500 times, of the inside frosted surface of a bulb embodying our invention.

An electric lamp bulb embodying the invention is designated l-inthe drawing and has its interior surface characterized by the presence of a multiplicity of acicular portions, by which term is meant elevations or projections of needle like or relatively long ridge like form running in differ- 55 cut directions, as distinguished from a frosted surface 2 frosted by a chemical etching with such surface having a cellular, octahedral or lens like formation. Furthermore, the crests and crevices appear to be sharp or angular as distinguished from rounded. It is the presence of the acicular structure to which is largely attributed the strength of the inside frosted bulbs, as it is found that when such formation is absent the bulbs in general are too fragile for commercial handling. The frosted surface of our bulb is further characterized and is distinguished from the cellular frosted surface produced by the double treatment method described in U. S. Patent No. 1,687,510 to Hpkin by the absence of rounded crevices.

A most important feature in inside frosted .bulbs of this character is that of strength to withstand breakage by impact, and in order to illustrate this feature the comparative strength tests hereinafter referred to were made on' an ordinary.

type of bump tester such as shown and described ,in said Pipkin Patent No. 1,687,510. It is found, as stated in said patent, that inside frosted bulbs which show an impact strength of '7' or more on such tester, when made up into lamps, are sufiiciently strong for commercial use. a

v The following strength readings, as determined by said tests, indicate for each set the average bump tester breakage point for twenty clear bulbs of each wattage taken at random from the same The average shown for each of the above vertical sets of figures is 57.5 for the clear bulbs; 12.3 for the inside frosted bulbs, and 21.7 for the percentage of strength of inside frosted bulbs to clear bulbs. Tests further show that these inside frosted bulbs do not weaken with age, which is an important feature.

If,- therefore, the average strength of clear bulbs to resist breakage by impact is 57.5, and the average minimum commercial strength requirement for inside frosted bulbs is 7, then it is apparent that inside frosted bulbs to resist breakage by impact should have an average strength of at least 12.15% of that of the clear bulb average. It is found that the strength of thefrosted ly, the frosted bulbs, before frosting, being as" bulbs varies with the extent to which the acicular projections or ridges are present.

Photometric tests were also made of certain wattage clear bulb lamps taken at random from regular stock and. of similar lamps having our inside frosted bulbs to determine the maximum brightness of each. Twenty-five and sixty watt lamps were used for thispurpose.

The average readings from these tests for the clear and inside frosted lamps'of both wattages were as follows:

Maximum Wattage brightness 15 5 Percent frosted In making the above brightness tests, three lamps were used for each test and the bulbs therefor taken at random from regular stocks of the same make of clear and frosted bulbs, respectivenearly like the clear bulbs as possible to obtain.

The results of the above strength and photometer tests showed the average for the twenty-five watt clear bulbs to be strength-42, and maxi-" mum brightness- 173. Lamps of twenty-five watt frosted on the inside and embodying our invention showed strength-10, and brightness 3.7. Clear lamps of sixty watt showed average strength--55, and brightness-605. Sixty watt lamps frosted on the inside and embodying our invention showed strength-12, and maximum brightness-12.9.

' A further test was made to determine the lumen output for lamps having clear bulbs as compared to lamps having inside frosted bulbs embody- In making the above lumen output tests, twelve bulbs were used in each of the tests and were taken at random from regular stock of the same.

make of clear and frosted bulbs, respectively, the frosted bulbs before frosting being as near like the clear bulbs as possible to obtain and such lamps each having a maximum brightness comparable to the above brightness readings.

The frosting solution preferably employed to produce 011 a lamp bulb an inside frosting having the characteristics above-pointed out may be divided into three parts, i. e., A the acid part,

' containing the acid and acidfluorides; 13" the crystalline part, containing the crystalline fluorides, sulphates and water, and .C the binder part, containing molasses for increasing the consistency of the compound and giving it the requisite viscosity.

(A) Part A preferably comprises the following. ingredients in substantially the proportions noted:

Ammonium acid fluoride.-- 33 lbs.3oz.

Hydrofluoric acid (approximately 60%) -10liters These materials are put into a drum of rubber, or other suitable acid resisting material, and rolled or agitated until complete solution takes place.

(B) Part "3 preferably comprises the following ingredients in substantially the proportions noted:

Sodium acid sulphate 11 lbs. 1 oz. Sodium fluoride 11 lbs. 1 oz. Water 6 liters These ingredients are put into a rubber mill preferably containing bronze balls. This material is milled usually for at least three hours, or until it contains no lumps or unground materials. At

the beginning of the run, pressure is generated in the mill by the chemical reaction which takes place therein, and care should be taken to release this pressure. The mill should be watched for about flfteen minutes for this purpose. It is preferable to use hot water toincrease the solubility of the materials. It is found that the hotter the water the more speedy the action.

(C) iart C preferably comprises:

Moms 12 liters tion, as hereinafter described. It is found that by applying water to the outside of a bulb during the etching operation and by varying the time, the flow and temperature of the water, the formation of the crystalline structure of the etched surface can be controlled.

When part 3" has been sufficiently milled, part A is added thereto and the whole is then preferably milled for at least half an hour or until a thorough mixing has taken place. This mixture is then turned into a wooden tub and part C added, stirring well while adding. The solution which is-now ready for use has a light brown creamy appearance and a consistency substantially equal to No. 10 motor oil.

The sodium fluoride contained in part B controls more or less the crystalline structure by stabilizing the viscosity of the solution. The s0dium fluoride does not dissolve to any great extent and the flne particles thereof in suspension in the solution form nuclei for crystal formation of ammonium, sodium and calcium silica fluorides (or fluosilicates). This crystalline structure is quite important in obtaining the desired strength characteristics ofan inside frosted bulb.

There is also another use for the sodium fluoride in the solution. When sodium acid sulphate is mixed with sodium fluoride in aqueous solutlon, an exothermic reaction takes place, causing heat to be given off. This reaction forms some free sulphuric acid, sodium sulphate, hydrofluoric acid and sodium acid fluoride along with sodium acid sulphate and sodium fluoride. All these substances are in, a 'state of delicate chemical balance, and it is believed that this equilibrium tends to stabilize the concentration of acid, sodium fluoride, sodium acid fluoride and sulphates in solution.

It is found that .part 3", when used alone, will etch the glass, but-the reaction is too slow for added, apower'ful frosting solution is. obtained and one which, when used in connection with the method hereinafter described, will produce an inside frosted bulb which is sufficiently strong against breakage to permit ordinary commercial handling, will effect a proper diffusion of light emitted therefrom to prevent objectionable glare or brightness, and will have a greater lumen output with consequent higher initial rating than other inside frosted bulbs now made of which we are aware.

In practicing our invention in the inside frosting of a lamp bulb, the frosting solution abovedescribed is first applied in stream or jet form under low pressure (about 1 /2 to 2 lbs.) ,up into. the interior of the bulb, so that the stream strikes the central top closed portion of the bulb, flows evenly down the sides and discharges from its lower open end. The solution is applied over a period of about ten seconds. i

Immediately following the application of the acid the bulb is subjected to an external hot water treatment to control the etching action of the acid adhering to the inner surface of the bulb. Hot water is caused to flow onto and down around the closed end of the bulb discharging from its lower end, and the temperatureof the water and time applied are important items in the etching operation in controlling the degree of etching and consequent acicular surface formation of the frost surface to produce the desired results. The temperature of the water preferably should be approximately 63 C., and the water should be of sufficient quantity to completely cover the bulb. The time of application varies, depending on the bulb size, but for most sizes the time is about ten seconds.

The bulb is next subjected to a thorough internal washing to entirely remove the etching acid therefrom and thus stop any further etching action. This washing is preferably accomplished by discharging a stream of water under relatively high pressure (about'15 lbs.) up into a bulb from a rather small orifice'iabout of an inch in diameter). For most satisfactory results the temperature of the water should be from 50 to After washing, the bulb is thoroughly dried preferably by directing hot air thereagainst, both inside and outside, and is then ready for use in a lamp. The bulb may also be held over a flame to facilitate drying. Nothing new is claimed for the washing and drying operation.

This application is filed as a continuation in part of our application Serial No. 93,246, filed July 29, 1936.

Having thus described our invention, what we claim as new, and desire to secure by United States Letters Patent, is:

1. A glass electric lamp bulb having its interior surface frosted by chemical etching so that the maximum brightness of an ordinary incandescent lamp comprising such bulb will be less than 20% of that of a like lamp with a clear bulb, said interior bulb surface being charac-' terized by the presence of acicular portions to such an extent that the strength to resist breakage by impact is greater than 13% of that of like clear bulb.

2. A glass electric lamp bulb having its interior surface frosted by chemical etching so that the maximum brightness of an ordinary incandescent lamp comprising such a bulb will be less than 15% of that of a like lamp with a clear bulb, said interior bulb surface being characterized by the presence of acicular portions to such an extent that the strength to resist breakage by impact is greater than 16% of that of a like clear bulb. 1

3. A glass electric lamp bulb having its interior surface frosted by chemical etching so that the maximum brightness of an ordinary incandescent lamp comprising such a bulb will be less than 15% of that of a like lamp with a clear bulb, said interior bulb surface being characterized by the presence of ridge-like elevations with sharp crests and crevices to such extent that the strength to resist breakage by impact is greater than 16% of that of a like clear bulb.

4. A glass electric lamp bulb having its interior surface frosted by chemical etching so that the maximum brightness of an ordinary incandescent lamp comprising such bulb will be less than 20% of that of a like lamp with a clear bulb, said interior'bulb surface being characterized bythe presence of a mulitiplicity of ridgelike elevations running in different directions to such extent that the strength to resist breakage by impact is greater than 13% of that of a like clear-bulb.

LYLE E. CALKINS. ORMONDE S. LEVI. 

